A generator called an alternator is provided in motor vehicles and supplies the electrical devices on board with energy and charges the vehicle battery. The alternator serves for the conversion of mechanical energy into electrical energy, with the required mechanical power being provided by the vehicle engine. With a running engine, the consumers are e.g. supplied directly with the power provided by the alternator. If the electrical power required in the vehicle is higher due to the switched-on consumers, the additionally required electrical power is e.g. taken from the vehicle battery. If the electrical power required by the vehicle is lower than the electrical power provided by the alternator, the surplus power is e.g. used to charge the battery.
Due to increasing electrification and automation, the number of the consumers to be supplied by the onboard network of the motor vehicle in this manner has greatly increased in recent times. Possible consumers are electrical controls, servo motors, air conditioning units, auxiliary heaters, main vehicle transmissions or transfer cases in all-wheel drive vehicles.
To be able to satisfy the increasing demands on the electrification in automotive construction without allowing the battery and alternator capacity to increase too much, energy management systems can be used which, on the one hand, allow the recovery of braking energy during thrust or brake phases of the vehicle. In such phases, the vehicle drives the alternator via the engine without fuel consumption, the alternator thereby producing more power than being consumed at that time as the case may be. This surplus energy is stored in the battery. On the other hand, such energy management systems can also be configured such that on a larger power demand for driving the vehicle, that is e.g. during acceleration phases, a greater portion of the energy supplied by the engine is used solely for driving the vehicle. The alternator is not active during such a phase and electrical consumers are only supplied via the battery. The alternator only becomes active again when the increased power demand for the driving of the vehicle is terminated.
Fluctuations in the onboard voltage can occur due to this regulation of the alternator. Fluctuations occur e.g. in the magnitude of 10.5 to 16V when the onboard voltage as a rule amounts to 13.5V.
When the onboard voltage of the vehicle falls below a nominal value, losses or larger setting times can be anticipated if e.g. an electrical actuator with a greater setting torque has to be switched, such as the actuator of the transmission.
This problem can be combated in part in that the power cross-sections with which the controllers and/or actuators are supplied can be enlarged or the inner resistances of the controllers can be reduced. In this manner, the voltage drop between the energy supply unit, that is the alternator or the vehicle battery, and the controller or the actuator is smaller. Higher weight to be moved and higher costs in particular arise due to the higher power cross-sections.